drm/amdgpu: fix scheduler timeout calc

scheduler timeout is in jiffies
v2: move timeout check to amdgpu_device_get_job_timeout_settings after
parsing the value
v3: add lockup_timeout param check. 0: keep default value. negative:
infinity timeout.
v4: refactor codes.

Signed-off-by: Flora Cui <flora.cui@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>